I want to make a "smooth" transition to a popup, when it is shown. It should scale, while beeing centered.

Here is what I came up with. Is this the best way to do things like this? I had to use a abstract Transition where I position the popup at the center, according to the current animation progress. I found it to be rather complicated, compared to other animation stuff, so I ask...

I saw something similar being done at the Devoxx, where some Oracle JavaFX developers presented their Kiosk. They said their code is available. Does anybody know where?